package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermDocs;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.util.FixedBitSet;

/**
 * A wrapper for {@link MultiTermQuery}, that exposes its
 * functionality as a {@link Filter}.
 * <P>
 * <code>MultiTermQueryWrapperFilter</code> is not designed to
 * be used by itself. Normally you subclass it to provide a Filter
 * counterpart for a {@link MultiTermQuery} subclass.
 * <P>
 * For example, {@link TermRangeFilter} and {@link PrefixFilter} extend
 * <code>MultiTermQueryWrapperFilter</code>.
 * This class also provides the functionality behind
 * {@link MultiTermQuery#CONSTANT_SCORE_FILTER_REWRITE};
 * this is why it is not abstract.
 */
public class MultiTermQueryWrapperFilter<Q extends MultiTermQuery> extends Filter {

    protected final Q query;

    /**
     * Wrap a {@link MultiTermQuery} as a Filter.
     */
    protected MultiTermQueryWrapperFilter(Q query) {
        this.query = query;
    }

    @Override
    public String toString() {
        // query.toString should be ok for the filter, too, if the query boost is 1.0f
        return query.toString();
    }

    @Override
    public final boolean equals(final Object o) {
        if (o == this)
            return true;
        if (o == null)
            return false;
        if (this.getClass().equals(o.getClass())) {
            return this.query.equals(((MultiTermQueryWrapperFilter) o).query);
        }
        return false;
    }

    @Override
    public final int hashCode() {
        return query.hashCode();
    }

    /**
     * Expert: Return the number of unique terms visited during execution of the filter.
     * If there are many of them, you may consider using another filter type
     * or optimize your total term count in index.
     * <p>This method is not thread safe, be sure to only call it when no filter is running!
     * If you re-use the same filter instance for another
     * search, be sure to first reset the term counter
     * with {@link #clearTotalNumberOfTerms}.
     * @see #clearTotalNumberOfTerms
     * @deprecated Don't use this method, as its not thread safe and useless.
     */
    @Deprecated
    public int getTotalNumberOfTerms() {
        return query.getTotalNumberOfTerms();
    }

    /**
     * Expert: Resets the counting of unique terms.
     * Do this before executing the filter.
     * @see #getTotalNumberOfTerms
     * @deprecated Don't use this method, as its not thread safe and useless.
     */
    @Deprecated
    public void clearTotalNumberOfTerms() {
        query.clearTotalNumberOfTerms();
    }

    /**
     * Returns a DocIdSet with documents that should be
     * permitted in search results.
     */
    @Override
    public DocIdSet getDocIdSet(IndexReader reader) throws IOException {
        final TermEnum enumerator = query.getEnum(reader);
        try {
            // if current term in enum is null, the enum is empty -> shortcut
            if (enumerator.term() == null)
                return DocIdSet.EMPTY_DOCIDSET;
            // else fill into a FixedBitSet
            final FixedBitSet bitSet = new FixedBitSet(reader.maxDoc());
            final int[] docs = new int[32];
            final int[] freqs = new int[32];
            TermDocs termDocs = reader.termDocs();
            try {
                int termCount = 0;
                do {
                    Term term = enumerator.term();
                    if (term == null)
                        break;
                    termCount++;
                    termDocs.seek(term);
                    while (true) {
                        final int count = termDocs.read(docs, freqs);
                        if (count != 0) {
                            for (int i = 0; i < count; i++) {
                                bitSet.set(docs[i]);
                            }
                        } else {
                            break;
                        }
                    }
                } while (enumerator.next());

                query.incTotalNumberOfTerms(termCount);

            } finally {
                termDocs.close();
            }
            return bitSet;
        } finally {
            enumerator.close();
        }
    }

}
